Lyme disease is caused by infection with the tick-borne spirochete Borrelia burgdorferi. Infection in humans is associated with various immunological abnormalities including elevated circulating immunoglobulins and hyperactive B lymphocytes, and can lead to the development of arthritis. The discovery that B. burgdorferi possesses a potent B cell mitogen and cytokine stimulatory activity could provide insight on the immunological abnormalities and on the pathology associated with infection. The host's response to the infecting organisms may also modulate the development of disease. The hypothesis to be addressed by this application is that the combination of cellular stimulatory activities produced by the spirochete and the inflammatory, or cytokine, response of the host work together in the development of arthritis. The B cell stimulatory and cytokine stimulatory molecules have been biochemically characterized as lipid modifications of proteins and co-purify with the outer surface lipoproteins osp A and osp B. This application proposes to characterize the lipid portions of these molecules, as there is strong evidence suggesting that the Borrelia synthesized lipids may contribute to the potency of osp A and osp B. Free fatty acids will be identified by Gas Chromatography and the composition of lipopeptides confirmed by Mass Spectroscopy. The receptor for the lipoproteins will be characterized by saturation binding analysis and identified by affinity chromatography with osp A and osp B. The biological effect of the lipoproteins on B lymphocytes and macrophages lineage cells will be carefully analyzed for responses that could be crucial to the development of disease. The animal model of Lyme disease will be utilized to determine the involvement of these bio-active lipoproteins in the development of arthritis. In the animal model infected mice of the C3H/HeJ strain develop severe arthritis whereas those of the BALB/c strain display only mild arthritis after infection. Purified lipoproteins will be injected directly into the joints of C3H/HeJ mice and histological developments monitored. Comparison of the arthritic and non-arthritic mice has suggested that production of INFgamma by C3H/HeJ mice may be associated with arthritis development. the involvement of INFgamma in the development of disease will also be determined directly by supplementing or neutralizing INFgamma in infected mice and monitoring the effect on arthritis development. The goal of these studies is to determine the involvement of the B. burgdorferi lipoproteins osp A and osp B in arthritis development and the role of INFgamma in this pathological process.